I understand that each testing location setup has a minimum of Windows (XP or later, Server 2003 or later); 32 or 64-bit; a dedicated PC (Pentium 4 or newer, 1GB RAM Minimum) or an equivalent VM. But, I'm not finding exacting specs of what is actually in use at each node.

Do these specs exist and I'm just missing them? If they don't exist, it would be great if they were made available since the setup itself can profoundly affect results/reporting.

They don't exist and there's no easy way to collect them (at least for VM's there is no way to know how constrained the host is that it is running on).

If you need or want consistent performance across nodes the only real way to do that is to use the Akamai EC2 locations, run a private instance or use something like Speed Curve where they use the same instance size across all locations (though they are limited to locations where EC2 nodes exist).